This is supply and demand. Olympus is out of production, so there are only a few new units in the hands of distributors and dealers. They all raised their prices $50. All production and distribution from Japan is impacted by the aftereffects of the tsunami, still. So I don't think this will get better soon.
About 3 months ago, after the newer housing for the E-PL2 came out, used housings showed up on eBay for $350-400. No more. Everything there is jacked up even higher than the $600 the legitimate dealers are charging for a PT-EP01.
The only real advantage of the older housing is that it will accommodate the EVF, but that's a useless accessory IMO. If I were looking for the housing today, I'd consider the newer camera and housing strongly, since support will be better near term. The new 14-42mm II lens on the E-PL2 is better. I retrofitted it on my E-PL1 and am very content.